A stent is commonly used as a tubular structure left inside the lumen of a duct to relieve an obstruction. Commonly, stents are inserted into the lumen in a non-expanded form and are then expanded autonomously (or with the aid of a second device) in situ. A typical method of expansion occurs through the use of a catheter mounted angioplasty balloon, which is inflated within the stenosed vessel or body passageway, in order to shear and disrupt the obstructions associated with the wall components of the vessel and to obtain an enlarged lumen.
In the absence of a stent, restenosis may occur as a result of elastic recoil of the stenotic lesion. Although a number of stent designs have been reported, these designs have suffered from a number of limitations. These include restrictions on the dimension of the stent.
Other stents are described as longitudinally flexible but consist of a plurality of cylindrical elements connected together. This design has at least one important disadvantage, for example, according to this design, protruding edges occur when the stent is flexed around a curve raising the possibility of inadvertent retention of the stent on plaque deposited on arterial walls. This may cause the stent to form emboli or move out of position and further cause damage to the interior lining of healthy vessels.
Thus, stents are known in the art. Such stents may be expanded during or just after balloon angioplasty. As a general rule, the manufacture of a stent will need to compromise axial flexibility in order to permit expansion and provide overall structural integrity.
Prior stents have had a first end and a second end with an intermediate section between the two ends. The stent further has a longitudinal axis and comprises a plurality of longitudinally disposed bands, wherein each band defines a generally continuous wave along a line segment parallel to the longitudinal axis. A plurality of links maintains the bands in a tubular structure. In a further embodiment of the invention, each longitudinally disposed band of the stent is connected, at a plurality of periodic locations, by a short circumferential link to an adjacent band. The wave associated with each of the bands has approximately the same fundamental spatial frequency in the intermediate section, and the bands are so disposed that the waves associated with them are spatially aligned so as to be generally in phase with one another. The spatial aligned bands are connected, at a plurality of periodic locations, by a short circumferential link to an adjacent band.
In particular, at each one of a first group of common axial positions, there is a circumferential link between each of a first set of adjacent pairs of bands.
At each one of a second group of common axial positions, there is a circumferential link between each of a second set of adjacent rows of bands, wherein, along the longitudinal axis, a common axial position occurs alternately in the first group and in the second group, and the first and second sets are selected so that a given band is linked to a neighboring band at only one of the first and second groups of common axial positions.
Furthermore, this stent can be modified to provide for bifurcated access, whereas the stent itself is uniform throughout. If the manufacturer designs such a stent to have an large enough opening, then it is possible to place the stent such that a pair of stents can be placed one through the other. In this fashion, the stents are capable of being placed at a bifurcation, without any welding or any special attachments. An interlocking mechanism can be incorporated into the stent design to cause the stent to interlock at the desired position during assembly of the device.
Further, a metallic stent has been designed which contains a repeating closed loop feature. The stent is designed such that the closed loop does not change dimensions during expansion. The composite stent is created by filling the area enclosed by the loops with a material that enhances clinical performance of the stent. The material may be a ceramic or a polymer, and may be permanent or absorbable, porous or nonporous and may contain one or more of the following: a therapeutic agent, a radio-opaque dye, a radioactive material, or a material capable of releasing a therapeutic agent, such as rapamycin, cladribine, heparin, nitrous oxide or any other know drugs, either alone or in combination.
It has been seen, however, that it may be desirable to provide for stents that have both flexibility to navigate a tortuous lesion as well as increased column strength to maintain the rigidity necessary after emplacement into the lumen of the body. The preferred designs tend to provide the flexibility via undulating longitudinal connectors. The rigidity is generally provided via the mechanism of slotted tubular stents. It is perceived that there may be mechanisms capable of enhancing the characteristics of these types of stents. Such a stent would be both flexible in delivery and rigid upon emplacement.
Furthermore, it is desirable to be able to produce stents in which the cross-sectional profile of either the struts or the connecting members is tapered (or variable) in size. In addition, it may be desirable to modify stents to have non-rectangular cross-sections. In both these cases, different manufacturing methods may aid in the creation of such stents.